The present invention relates to a contact element for a power switch which, in order to open or close the switch, cooperates with an opposing contact element that has the shape of a ring and in which a rotating electric arc forms when the switch is opened.
Electric arcs cause the base points of the electrodes to be heated considerably. To realize low consumption, particularly with strong current arcs, means must be provided to cause the base points of the arcs not to form at one point on the electrodes but to move over the surface of the electrodes.
It is known to configure contact elements for vacuum switches so that a thick-walled hollow cylindrical contact element is provided which has cuts distributed over its circumference, with such cuts, seen from the top, extending at an angle to the radii and, seen from the side, obliquely toward the normal on the contact surface.
If an arc burns between such contact elements, a force component is created on the arc which causes the arc to rotate. However, the arc moving from one such segment over a cut to the next segment causes great consumption at the edges of the segments.
A modification of this embodiment is disclosed in the in-house periodical of AEG, "Vakuum-Leistungsschalter--ein neuer Weg im Bereich der Mittelspannung", [Vacuum Power Switches--A New Way In The Medium Voltage Domain], A 24.05.15/0381, page 8. This improvement provides a ring at the frontal face of the hollow cylindrical contact element, i.e. in the contact region. Although this results in less consumption, it also results in unsatisfactory operation. Reliable rotation of the arc at a rate of rotation sufficient to reduce consumption cannot be realized with relatively low current intensities. The arc rotates reliably and at a sufficient speed only if a comparatively high current is exceeded because a component of the current flows through the ring of such an arrangement, also in a direction opposite to the rotary movement, annd this component causes electromagnetic forces to be generated which counteract the rotation of the arc.